The top five reasons why cars fail their MOT and how to avoid them

13 March 2017

By Rebecca Milligan

All vehicles more than three years old need an annual MOT. We asked some of our Which? Trusted trader garages about the most common faults.

An MOT is a government-mandated test of vehicles more than three years old, to check for faults that would make a car unsafe on the road. Some traders told us that they have known customers confuse it with a service. Victory Auto Services’ Wayne Adams said: ‘An MOT isn’t the same as servicing, it’s basically a government test and there are quite strict processes to go through.’

During a service, your garage will do a thorough inspection of the vehicle - this can include putting the car on a jack, taking the wheels off, stripping the brakes, measuring the fluids and so on. Llanishen MOT & Service Centre Ltd’s Richard Babbage said: ‘An MOT is only really a visual inspection. It’s nowhere near as thorough as a service.’

Many people will leave it to the last minute to take their car in for an MOT. But as Tim Bartlett from AVW told us: ‘People don’t realise they can bring the car in up to a month early without losing out. If you bring it in early, you have time to sort out any problems, without it being a last-minute distress purchase.’

Top five common faults

The government collects and compiles the statistics behind MOT failures nationally, and each year the DVSA (Driver Vehicle Standards Agency) releases the figures. Here are the latest top five most common faults based on tests done between April 2015 and March 2016[1]:

1. Lighting and signalling (18.9%)

This was the most common fault, found in just under one in five MOTs. This was backed up by our Which? Trusted traders – everyone we spoke to mentioned lights or bulbs as a common fault. It is one of the easiest to avoid - a quick look around the car should be enough to tell you if your lights are working.

Tim Bartlett from AVW told us: ‘Over the years we’ve learned to use only the best-quality bulbs, because they’re such a pain to change - particularly on modern cars.’ But it’s not surprising that even the best bulbs wear out. Tim says: ‘They’re constantly being jiggled about, they go hot and cold, they get wet and damp, so there’s a lot can go wrong there.’

Slightly more complicated to check is ‘headlight aim’ – when the light is not pointing in the right direction. Llanishen MOT & Service Centre Ltd’s Richard Babbage explained that this can often come up as a fail because of poor fitting. He said: ‘Lights can be out of focus, or they’ve been fitted by an auto centre that will bang the lights in, charge the customer £8 or £10, and send them on their way without putting the bulb in properly.’

2. Suspension (13%)

Our Which? Trusted traders agreed with the official figures - almost all of them listed suspension as one of the most common faults. Several mentioned the vulnerability of small rubber joints or bushes – these reduce the impact of metal on metal parts, so are particularly prone to wear and tear.

Suspension is not something you can easily check yourself at home. But if you see unusual tread-wear patterns on your tyres, or your steering is not as smooth as usual, this can be a sign of a suspension problem.

3. Brakes (10%)

One in ten vehicles tested had brake issues. Garages will visually check the condition of brake pads, and all our Which? Trusted traders identified brakes as an area commonly found at fault.

Although your MOT can identify brake problems, an MOT is not a full test. Brake testing can be particularly problematic if mechanics can’t see the brake pads clearly. Llanishen MOT & Service Centre Ltd’s Richard Babbage says: ‘An MOT can only give a snapshot of a car’s condition. If cars have alloy wheels on, and you can’t see the state of the brake pads, you can only know how well the brakes perform at the time of the test.’ This is one reason it’s so important to have your car serviced regularly in addition to your MOT.

4. Tyres (8%)

Tyres will wear from general use, but they will also wear unevenly if there are other problems with the car, such as the suspension or the alignment of the wheels. John Matthews from Wheels 4 Plus 2 Ltd told us about a customer whose new tyres had worn out after only three months, because the wheel alignment was incorrect.

Several traders told us about seeing tyres that were practically down to canvas. Ideally you should check your tyre tread regularly yourself, rather than wait for a service or MOT.

The 20p test is pretty simple and takes only a minute to do. Place a 20p coin into the main tread grooves of your tyre; the tyre tread should reach the outer band of the coin. Check at least three locations around each tyre from the centre to the rim. If you can see the outer band of the coin, get your tyres checked by a qualified tyre professional.

5. Driver’s view of the road (7%)

Issues affecting the driver’s view of the road were almost as frequent as tyre trouble. Frayed or broken windscreen wipers and smeared or chipped windscreens constitute a fail here.

Additionally, many people don’t realise there are strict rules about the size of objects allowed on the windscreen that could affect the driver’s view. Brian Cartwright from Wolf Garage Ltd explained: ‘If you think of your steering wheel and where the windscreen wiper works, any chips or cracks in the area from 9am to 3pm cannot be bigger than 10mm in diameter. Outside that area, still in the wiper zone, you can’t have anything larger than 40mm in diameter on the windscreen.’

This means that air fresheners dangling from the rear-view mirror and sat navs in the middle of the windscreen can constitute an MOT fail.

Some car makes and models have particular areas that are more vulnerable to wear and tear. You can check the Which? guide to the most reliable car brands to find out more.

Advice from Which? Trusted traders

Our Which? Trusted traders’ experience bears out the statistics, with lights, tyres and suspension being mentioned by nearly all the traders we spoke to. There were also a few other issues that came up.

John Matthews from Wheels 4 Plus 2 Ltd mentioned that the diesel particulate filter (DPF) would often clog on diesel vehicles that were just used as runabouts around town. John said: ‘Diesels are designed to be workhorses, up and down the motorway… and if they’re not driven hard the filter clogs up.’ These are expensive to fix but you can prevent the problem by running your diesel vehicle on the motorway, at speed, for about 20 minutes once a week.

Andrew Weed from Abergavenny Auto Repairs suggested taking a careful look at your seatbelts. He said: ‘The front ones will probably be OK but, if customers don’t carry a passenger very often, then there can be a problem with the back one. Another thing you’ll find is that they’ve had a dog in the back that has chewed the seatbelt.’

Rob Stanton from Court Vehicle Services recommended checking your number plates aren’t cracked or damaged. More than one trader mentioned making sure your car was clean, and areas that needed to be examined were clear. Brian Cartwright from Wolf Garage Ltd said: ‘If there’s baggage in the boot, then we can’t test it. We’ll move it if it’s big boxes, but not when it looks like someone’s living out of their car.’

Several garage owners mentioned ensuring that liquids in the vehicle were topped up. Keith Jackson from InTune Garage Services told us: ‘People will come in with no liquid in their washers, so they don’t work.’

And finally, make sure there’s some fuel in the vehicle. The garage will need to do an emissions test, which is impossible if they can’t run the car.